Characteristic Reactions of Barium (Ba²⁺)

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Barium, \(\ce{Ba^{2+}}\)
Most common oxidation state: +2
M.P. 725º
B.P. 1640º
Density 3.51 g/cm³
Characteristics: Barium is a silvery metal. Extremely active, reacts quickly with oxygen in air, and with most non-metals.

Sulfate Ion

Addition of a sulfate source, such as sulfuric acid produces a white, finely divided precipitate of barium sulfate:

\[\ce{Ba^{2+}(aq) + HSO4^{-}(aq) <=> BaSO4(s) + H^{+}(aq)} \nonumber \]

\[\ce{Ba^{2+}(aq) + SO4^{2-}(aq) <=> BaSO4(s)} \nonumber \]

\(\ce{BaSO4}\) is extremely insoluble in water, alkalies, or acids, but is slightly soluble in hot, concentrated sulfuric acid.

Ammonium Carbonate

A soluble carbonate such as ammonium carbonate reacts with \(\ce{Ba^{2+}}\) to precipitate white barium carbonate:

\[\ce{Ba^{2+}(aq) + CO3^{2-}(aq) <=> BaCO3(s)} \nonumber \]

Aqueous ammonia should also be added to ensure complete precipitation. The aqueous ammonia assures that the concentration of carbonate ion will be high enough by preventing the hydrolysis of carbonate ion to form hydrogen carbonate ion:

\[\ce{NH3(aq) + H2O(l) <=> NH4^{+}(aq) + OH^{-}(aq)} \nonumber \]

\[\ce{CO3^{2-}(aq) + H2O(l) <=> HCO3^{-}(aq) + OH^{-}(aq)} \nonumber \]

Barium carbonate is soluble in acid, including dilute acetic acid, in strong bases, and in aqueous ammonia.

Potassium Chromate

Soluble chromates react with barium ion to form a finely divided yellow precipitate of barium chromate:

\[\ce{Ba^{2+}(aq) + CrO4^{2-}(aq) <=> BaCrO4(s)} \nonumber \]

Barium chromate is soluble in mineral acids, but only slightly soluble in acetic acid. In strong acids, an orange solution of barium dichromate is formed:

\[\ce{2BaCrO4(s) + 2H^{+}(aq) <=> 2Ba^{2+}(aq) + Cr2O7^{2-}(aq) + H2O(l)} \nonumber \]

Barium chromate is insoluble in bases.

Sodium Oxalate

Soluble oxalates react with barium ion to produce white barium oxalate. This precipitate is soluble in strong acids, and in hot dilute acetic acid.

\[\ce{Ba^{2+}(aq) + C2O4^{2-}(aq) + H2O(l) <=> BaC2O4 \cdot H2O(s)} \nonumber \]

Flame Test

Solutions of barium salts give a yellow-green color to a Bunsen burner flame.

No Reaction

\(\ce{Cl^{-}}\), \(\ce{NH3(aq)}\) in dilute solutions (< 0.2 M), \(\ce{NaOH}\) in dilute solutions (< 0.2 M)